Well, keep in mind that a lot of native speakers can't grasp the nuances of the English language. Also there's a difference between proper/academic English (usually written) and spoken (which will be influenced by dialects). We don't speak in proper grammar most of the time (at least not that I've noticed) and we don't necessarily use proper grammar in casual written communication. Also, at least in the US, grammar doesn't seem to be taught much before college. At least I don't remember that happening. Basically, by learning English as a second language, you might actually have a more comprehensive knowledge of proper grammar than a native speaker (at least in the US).

Back to your original question, I was pretty sure you were right (and the movie was just reflecting how English is usually spoken...at least from my experience). I mean, I know proper grammar for the most part (it's annoying complex), but I'm not usually going to worry about it when I speak. Especially in casual conversation. The point is, everyone still knows what you mean.

I don't know if that makes any sense at all.